Flexural strengthening of fire-damaged reinforced concrete continuous T-beams with CFRP sheets

Experiments of seven reinforced concrete (RC) two span T-beams were introduced. During the experiments, one T-beam was normal temperature control T-beam, and the other six T-beams were heated under ISO-834 standard fire. All T-beams had the same geometrical dimensions and reinforcement as well as the loading and support arrangement. The fire-damaged T beams were classified into two groups according to the fire exposure time. Different fire exposure time including 60 minutes and 75 minutes were investigated. In each group, one T-beam was unstrengthened fire-damaged control T-beam, and the other two T-beams were strengthened with carbon fiber reinforced polymer (CFRP) sheets after fire. The results showed that midspan yield load, ultimate load, stiffness and ductility of the fire-damaged T-beams decreased comparing with these of the normal temperature control T-beam, while ductility and stiffness dropped more sharply. External strengthening with CFRP sheets was found to increase the load capacity and stiffness of T-beams, but the ductility of T-beams dropped. Different from the normal temperature T-beam, the fire-damaged T-beams had obvious moment redistribution at the beginning of the loading because of the variable stiffness along the length of the T-beams. The moment redistribution of fire-damaged RC continuous T-beams changed greatly because of the influence of fire. Under the same heating curve, fire exposure time was one important factor that influences the moment redistribution of fire-damaged RC continuous T-beams. The way of strengthening using CFRP influenced the moment redistribution of the fire-damaged RC continuous T-beams. Tensile rupture of the CFRP sheets was the main failure mode for the strengthened fire-damaged RC continuous T-beams. The relationship between stiffness ratio and moment ratio of the continuous beams was deduced as well.